The present invention relates in general to fuel injection systems in turbomachines.
The fuel injection system in a turbomachine comprises a high pressure pump for pressurizing the fuel coming from a fuel tank, a plurality of fuel injectors disposed in a combustion chamber of the turbomachine, and interposed between those two sets of elements, a fuel metering unit for controlling the rate at which fuel is to flow into the injectors from the high pressure pump.
Conventionally, the metering unit comprises both a stop valve for ensuring that fuel is delivered to the injectors only once a predetermined minimum pressure has been reached, and also means for adjusting the flow rate of the fuel, which adjustment means come into action above said minimum pressure as a function of various parameters concerning the turbomachine as supplied by a computer. French patent application No. 2 718 190 filed by the Applicant describes one such conventional system. During the stage of starting the turbomachine, fuel is pumped from the tank and is sent towards the metering unit. Once the minimum pressure has been reached, the adjustment means are activated and the stop valve opens, thereby delivering fuel to the injectors. It is then possible to control the flow rate continuously as a function of engine parameters by acting on the adjustment means.
Although that injection system gives general satisfaction, it nevertheless presents certain drawbacks. In particular, it takes no account of the turbomachine operating at different speeds, which can lead to certain components of the system being overdimensioned and to a harmful increase in fuel temperature.
The present invention seeks to mitigate those drawbacks with an injection system that limits fuel heating and that enables its components to be dimensioned optimally.
These objects are achieved by a fuel injection system in a turbomachine, the system comprising a high pressure pump for pressurizing the fuel coming from a fuel tank to a high pressure P1, a plurality of fuel injectors disposed in a combustion chamber of the turbomachine, and a metering unit interposed between said high pressure pump and said plurality of injectors to control the rate at which fuel flows into the injectors from the high pressure pump, wherein said metering unit comprises a pressurization valve piloted to occupy two pressure levels by means of a metering valve fed with fuel from said high pressure pump.
With these two pressure levels controlled by the metering unit valve, the pressure in the fuel circuit is limited at low flow rates, and maximum pressure is used only when the turbomachine is consuming high flow rates.
The pressurization valve comprises a first end inlet connected to a first load outlet of said metering valve, and a second end inlet opposite said first end inlet and connected firstly to said high pressure pump via a first diaphragm and secondly to a second load outlet of said metering valve via a third diaphragm, fuel feed to said injectors connected to a pilot outlet of said pressurization valve resulting from the unbalance in the pressures applied to the two end inlets thereof under the control of a computer.
Preferably, the metering valve comprises a hydraulic slide which can be moved linearly under the control of said computer and having two annular grooves serving to establish communication respectively between a first feed inlet and said first load outlet, and secondly between a second feed inlet and said second load outlet.
Advantageously, the metering unit further comprises a solenoid stop valve for acting on said pressurization valve to interrupt the fuel feed to said injectors. Said solenoid stop valve comprises a first inlet connected to said high pressure pump, a second inlet connected to low pressure P2 via a second diaphragm, and an outlet connected to said second end inlet of the pressurization valve.